1. Field of the Invention
The present invention relates to door lock systems using electronic and mechanical elements in which the keys are often changed, for example daily, and more particularly to such a system which may be retrofitted into a wide variety of existing mechanical door locks.
2. Discussion of Related Art
At the present time, the most widely used door lock system for houses uses a key having a pattern of grooves and an indented top surface. To unlock the door, the key is fitted into a keyhole and lifts small spring-loaded pins to enable a cylinder to be turned. The turning of the cylinder releases a latch and/or slides a bolt to unlock the door.
That type of lock, although relatively inexpensive, is subject to "picking", in which a thief, without a key, unlocks the door. In addition, that type of lock, when used in hotels, motels and other public facilities, may readily be opened by thieves or others whose entry in the rooms is not authorized, because the system will have a master key which will open a series of locks. However, the master key is as easily duplicated as any other key and there have been many instances of master keys falling into the hands of thieves and other unauthorized persons.
Because of its lack of security, simple key-operated locks are often not used in industry, offices and in hotels. Instead, they may use various types of electronic locks.
One type of electronic lock uses a numerical keypad which requires the entry of a number to release the lock. U.S. Pat. No. 4,148,092 shows this type of lock system. Such keypads are not used by hotels, since it is difficult to change their working numbers and the hotel guests may change daily.
A system widely used in hotels involves a card issued to the guest when he/she checks into the hotel. The card is inserted into an electronic card reader which reads the holes or magnetic strips or other magnetic patterns on the card. The door is unlocked if the pattern matches the number entered into the card reader for that day. This type of system is shown, for example, in U.S. Pat. Nos. 3,926,021; 4,717,816; 4,742,426; 4,802,353; 4,534,194; and 4,766,433.
One type of electronic lock system uses a central computer which communicates by wire to the lock mechanism at each door. A hotel office may have a special device which will punch cards or form magnetic areas on magnetic cards. The lock combination on the cards is in the form of digital bits and may be changed daily. The system is interactive because each time someone uses the system by opening an electronic lock, the entry is recorded in the log of the central computer and the operator may print-out a list of the persons who entered each room and the time they did so. This wired system, however, is expensive as it requires an expensive central computer, wiring of the system, and a relatively expensive machine to punch or magnetically mark the cards.
In an alternative system, each door has a radio transmitter which transmits the data information to a receiver connected to the central computer. However, it is subject to radio interference and is a relatively expensive system. A less expensive alternative is a non-interactive system. Each of the electronic door locks is independent and battery-operated. A machine at the central office, for example, the lobby desk of the hotel, will place the code on punch cards or magnetic cards, which is relatively expensive, since the machines to produce the code on such cards are costly. Each card is inserted into the card-reading mechanism which will read the punched holes or the magnetic marks. The first card insertion sets up the code within a lock. To open the lock, the user must again insert the card. Since the system is not interactive, there is no way, using the returned cards or other cards, to tell who has opened the lock or the time or date of any entries.
It has also been suggested that a "smart card" may be used in a security system. A smart card is a plastic card having an integrated circuit ("chip") embedded in it. The chip has a code which is read by the card reader. Such smart cards may present a problem in reliability because they use a series of contacts on an edge of the card, and those contacts may become dirty or worn.
It has also been suggested, in U.S. Pat. Nos. 4,297,569; 4,779,090; 4,326,125 and 4,712,398, that the chip may be embedded in a key, instead of a smart card. It is known to use an integrated circuit in a button casing for use in production and inventory control, for example, to track engines through a production line.
In U.S. Pat. No. 5,113,675 to Uyeda, the lock may be unlocked either by a conventional key or a card. A cam 72 operated a locking plate 60 having a tooth 64 which may be engaged in notch 75.
In U.S. Pat. No. 4,982,587 to Tzou, a conventional key operates pins which act on switches.
U.S. Pat. No. 4,703,163 to Genest shows an energy-saving circuit in a card reader type of electronic lock.